1. Field of the Invention
Embodiments of the present invention relate, in general, to inter-cell communications in a wireless regional area network and particularly to using Time Division Multiple Access (“TMDA”) Coexistence Beaconing Protocol for inter-cell discovery and communications.
2. Relevant Background
Cells of a Wireless Regional Area Network (“WRAN”) overlap to form a seamless communication environment in which users operating consumer premise pieces of equipment (“CPE”) can travel from one cell to another without loss of connectivity. While simple in concept, the reality of making such an overlapping system of cells operate efficiently is very complex. Many techniques to manage simultaneous communication have been used including Time Division Multiple Access (TDMA).
TDMA is a scheme that subdivides the available frequency band into one or more channels. These channels are further divided into a number of physical channels called frames. Using TDMA, overlapping WRAN cells can operate on one or more channels while allowing CPEs to communicate simultaneously. CPEs communicate with each other, and to some extent, with a base station, via packets sent via a frame. To the extent that two WRAN cells operate on the same channel, CPEs can communicate using Coexistence Beaconing Protocol (“CBP”) packets in which their self-coexistence window (“SCW”) is synchronized.
FIG. 1 shows a typical frame sequence of two WRAN cells operating on the same channel as is known in the prior art. As shown, WRAN cell number 1 (WRAN1) 110 and WRAN cell number 2 (WRAN2) both operate on channel A. The channel is divided into a number of frames and each frame includes a plurality of SCWs that convey what a particular WRAN cell is doing at any point of time and data. These frames are known in the art as packets. During an active mode 130, 140 a cell is transmitting its data. This is shown in FIG. 1 by the three 111s with respect to WRAN1 and three 222s with respect to WRAN2. As shown, WRAN1 is transmitting during an active mode in the first frame and WRAN2 is in a passive or receiving mode 150. Similarly, in the second frame WRAN2 is in an active mode 140 and WRAN1 is in a passive mode 160. However this sort of configuration (one in which one WRAN is transmitting and the other is receiving) is not always guaranteed.
The third frame of FIG. 1 shows a condition where both WRAN1 110 and WRAN2 120 are transmitting at the same time 170. A collision occurs and no data is transferred. Similarly, situations can exist where the WRANs are both in passive mode 180 again resulting in no transfer of data. The current state of the art for communication of CBP packets using synchronized SCWs is, as is known in the art, best effort or contention based communication. Each WRAN continues to try to transmit randomly until a non-collision event occurs that allows the transmission to succeed. As one skilled in the art will recognize, such an approach is inefficient.
As one would expect, the problems identified above are compounded when multiple channels are considered. As will be appreciated by one skilled in the art, when multiple channels are used, a WRAN cell can only transmit on one channel but can receive on several. FIG. 2 shows a typical frame sequence of two WRAN cells operating on different channels using CBP as is known in the prior art. As before, WRAN1 210 is operating on channel A; however, this time WRAN2 220 is operating on channel B. Thus, for information to be conveyed, not only must a collision not exist but both WRANs must be operating on the same channel. Thus, while in the first frame 230 WRAN1 210 is active and transmitting on channel A and WRAN2 220 is operating in a passive mode, no captures occurs since WRAN2 is listening on channel B. Likewise, in frame 240 WRAN2 220 is transmitting on channel B but a capture of data is again wanting as WRAN1 210 is listening on channel A. Indeed several frames may pass until the two WRAN cells are operating in a combination that permits data transfer.
As the best effort process of cross-channel CBP communication continues, several frames pass with both WRAN cells operating in a passive mode. Eventually, WRAN1 210 will transmit 250 on channel A and WRAN2 will be listening on channel A enabling a capture. Likewise, when WRAN2 transmits on channel B 260 and WRAN1 is listening on channel B another capture will occur. Communication between two neighboring cells can succeed only when at least two CBP-enabled stations from different cells are tuned to the same channel during a SCW with one of them transmitting and the other receiving.
As with a single channel CBP process, cross channel communication is contention based. A challenge exists to coordinate multiple channel communication between CBP-enabled stations of differing neighboring cells.